Biotransformation of terodiline I. Identification of metabolites in dog urine by mass spectrometry

Drug disposition of chiral and achiral drug substrates metabolized by cytochrome P450 2D6 isozyme: case studies, analytical perspectives and developmental implications

The concepts of drug development have evolved over the last few decades. Although number of novel chemical entitities belonging to varied classes have made it to the market, the process of drug development is challenging, intertwined as it is with complexities and uncertainities. The intention of this article is to provide a comprehensive review of novel chemical entities (NCEs) that are substrates to cytochrome P450 (CYP) 2D6 isozyme. Topics covered in this review aim: (1) to provide a framework of the importance of CYP2D6 isozyme in the biotransformation of NCEs as stand-alones and/or in conjunction with other CYP isozymes; (2) to provide several case studies of drug disposition of important drug substrates, (3) to cover key analytical perspectives and key assay considerations to assess the role and involvement of CYP2D6, and (4) to elaborate some important considerations from the development point of view. Additionally, wherever applicable, special emphasis is provided on chiral drug substrates in the various subsections of the review.

Identification of the biliary metabolites of (+/-)-3-dimethylamino-1,1-diphenylbutane HCl (recipavrin) in rats

1. The in vivo biliary metabolites of (+/-)-3-dimethylamino-1,1-diphenylbutane hydrochloride (recipavrin) isolated from Wistar rats have been characterized by g.l.c.-mass spectrometry. 2. Non-conjugated metabolites include recipavrin (1), norrecipavrin (2), diphenylbutanone (3), diphenylbutanone oxime (4), diphenylbutanone phenol (12), diphenylbutanone oxime phenol (14), recipavrin phenol (19), diphenylbutanone O-methylcatechol (16) and diphenylbutanone oxime O-methylcatechol (18). 3. Following beta-glucuronidase hydrolysis and extraction from pH 10 solution, diphenylbutanone (3), diphenylbutanone oxime (4), an unidentified compound (6), primary amine (8), norrecipavrin (2), recipavrin (1), phenols (12, 14, 15), norrecipavrin phenol (13), O-methylcatechols (16, 18), diphenylbutanol O-methylcatechol (17), recipavrin O-methylcatechol (19) and a secondary formamide (5) were identified by g.l.c.-mass spectrometry. 4. Various extraction solvents were employed in sample workup. The formamide (5) was present regardless of solvent used, while the trace presence of secondary acetamide (7) may be associated with the use of ethyl acetate. 5. Metabolites isolated after beta-glucuronidase hydrolysis were characterized by g.l.c.-mass spectrometry of the underivatized form, and as the trimethylsilyl (TMS) derivatives, or following methylation with diazomethane or trimethylanilinium hydroxide (TMAH).

Pharmacokinetics of terodiline and a major metabolite in dogs with a correlation to a pharmacodynamic effect

The pharmacokinetics and pharmacodynamics of the anticholinergic and calcium antagonistic drug terodiline, N-tert-butyl-1-methyl-3,3-diphenylpropylamine, have been studied in beagle dogs. The bioavailability was about 25% (0.15 and 0.5 mg/kg), the terminal half-life 3 hr, the systemic clearance 40 ml/min..kg, the volume of distribution (V beta) about 7 l/kg and the unbound fraction in serum 0.14. p-Hydroxyterodiline and p-hydroxy-m-methoxyterodiline were quantitated and constituted 15-40% and 25%, respectively, of the amount excreted in urine (about 60% of the dose) and were the main metabolites, as in man. The dog was used as an experimental model to study the chronotropic effect. An increased heart rate was observed after acute administration of high doses of terodiline as well as after p-hydroxyterodiline. A 20% increase in heart rate was observed at a mean serum concentration of 1086 and 1010 micrograms/l following intravenous injection of terodiline or p-hydroxyterodiline, respectively. The corresponding unbound concentrations were 150 and 474 micrograms/l. The potency ratios of terodiline/p-hydroxyterodiline was 0.9 +/- 0.2 (based on total concentrations) and 3.2 +/- 0.8 (based on unbound concentrations). The estimated potency of parent drug and main metabolite and the fact that p-hydroxyterodiline constitutes 10-20% of the terodiline steady-state level in man, indicate that the contribution of the metabolite to the chronotropic effect observed in clinical studies is minor.

Biotransformation of aliphatic formamides: metabolites of (+-)-N-methyl-N-(1-methyl-3,3-diphenylpropyl) formamide in rats

The in vivo biliary and urinary metabolites of (+-)-N-methyl-N-(1-methyl-3,3-diphenylpropyl) formamide (1) from male Wistar rats have been characterized by gas chromatography/mass spectrometry. In urine, non-conjugated metabolites included 1,1-diphenyl-3-butanone (4) and 3-methylamino-1,1,diphenylbutane (7). beta-Glucuronidase liberated 4, 1,1-diphenyl-3-butanol (5), 1,1-diphenyl-3-butanone oxime (6), N-hydroxymethyl-N-(1-methyl-3, 3-diphenylpropyl) formamide (3), 1-(4-hydroxyphenyl)-1-phenyl-3-butanone (11), 1-(4-hydroxyphenyl)-1-phenyl-3-butanone oxime (12), N-methyl-N-(1-methyl-3-(4-hydroxyphenyl)-3-phenylpropyl) formamide (8), 1-(4-hydroxy-3-methoxyphenyl)-1-phenyl-3-butanone (16); 1-(4-hydroxy-3-methoxyphenyl)-1-phenyl-3-butanol (17), 1-(4-hydroxy-3-methoxyphenyl)-1-phenyl-3-butanone oxime (18), N-(1-methyl-3-(4-hydroxy-3-methoxyphenyl)-3-phenylpropyl) formamide (14) and N-methyl-N-(1-methyl-3-(4-hydroxy-3-methoxyphenyl)-3-phenylpropyl) formamide (13). Most of the carbinolamide (3) decomposed in the gas chromatograph inlet to N-(1-methyl-3,3-diphenylpropyl) formamide (2) unless stabilized as a trimethylsilyl (TMS) derivative. In bile, compounds 1, 2, 3, 5, 6, 11, 12 and 16 were present as non-conjugated metabolites. beta-Glucuronidase also liberated N-(1-methyl-3-(4-hydroxyphenyl-3-phenylpropyl) formamide (9), and all of the previously listed compounds except 7. Trimethylsilylation of the conjugated bile fraction revealed the presence of an additional two compounds: N-hydroxymethyl-N-(1-methyl-3-(4-hydroxyphenyl)-3-phenylpropyl) formamide (10) and N-hydroxymethyl-N-(1-methyl-3-(4-hydroxy-3-methoxyphenyl)-3-phenylpropyl ) formamide (15). A stable carbinolamide metabolite standard was synthesized and the mass spectral fragmentations of its TMS derivative studied by tandem mass spectroscopy. This is the first report on stable carbinolamide metabolites of high-molecular-weight formamides.

Biotransformation of terodiline. V. Stereoselectivity in hydroxylation by human liver microsomes

The stereoselective hydroxylation of N-tert-butyl-4,4-diphenyl-2-butylamine (Terodiline) was studied in human liver microsomes. Formation of the two main metabolites, N-tert-butyl-4(4-hydroxyphenyl)-4-phenyl-2-butylamine (II) and N-(2-hydroxymethyl-2-propyl)-4,4-diphenyl-2-butylamine (VI), was found to be stereoselective. R-Terodiline was preferentially transformed by phenolic hydroxylation to the 2R,4S-II and 2R,4R-II forms with a pronounced selectivity for the former. The formation rate ratio 2R,4S-II/2R,4R-II was about 6, obtained from two liver preparations. S-Terodiline was mainly hydroxylated to the alcohol 2S-VI although phenolic hydroxylation to the 2S,4S-II and 2S,4R-II also occurred, yielding about equal amounts of the two phenols.

Biotransformation of terodiline. III. Opposed stereoselectivity in the benzylic and aromatic hydroxylations in rat liver microsomes

1. Terodiline (N-tert-butyl-4,4-diphenyl-2-butylamine) is a racemic drug with anticholinergic and/or calcium antagonistic activity, which is subject to renewed interest as a potential remedy for urinary incontinence. As part of the current investigations on terodiline, the metabolism of its enantiomers is being investigated. 2. The metabolism of the enantiomers of terodiline in rat liver microsomes is slow, as for the racemate, though the S-enantiomer is metabolized more rapidly than its optical antipode. Phenobarbitone pretreatment of the rats enhances the metabolism with a marked increase in the conversion of the S-enantiomer. 3. While aromatic p-hydroxylation greatly exceeds benzylic oxidation in the metabolism of R-terodiline, this situation is reversed in the metabolism of S-terodiline. Moreover, the rate of aromatic p-hydroxylation of racemic terodiline follows that of R-terodiline, while the rate of benzylic hydroxylation of racemic terodiline follows that of S-terodiline. Phenobarbital pretreatment of the rats had little or no effect on aromatic p-hydroxylation but markedly increased benzylic oxidation. 4. Separation of the mixture of p-hydroxylated metabolites into diastereomeric pairs showed that their composition is highly dependent on which form of terodiline is used as substrate. 5. The results from the study are compatible with the participation of multiple forms of cytochrome P-450 enzymes.